Ability to genetically manipulate the loss of green colour during grain maturation has potentials for increasing productivity, disease resistance, and drought and heat tolerance in crop plants. Two doubled haploid, tworowed barley populations (Vlamingh 9 Buloke and VB9524 9 ND11231*12) were monitored over 2 years for loss of green colour during grain filling using a portable active sensor. The aims were to determine the genomic regions that control trait heritability by quantitative trait locus (QTL) analysis, and to examine patterns of QTLenvironment interactions under different conditions ofwater stress. In the Vlamingh 9 Buloke cross, broad-sense heritability estimate for loss of green colour (measured as the difference in sensor readings taken at anthesis and maturity, DSRI) was 0.68, and 0.78 for the VB9524 9 ND11231*12 population. In the VB9524 9 ND11231*12population, rapid loss of green colour was positively associated with grain yield and percent plump grains, but in the Vlamingh 9 Buloke population, a slower loss of green colour (low DSRI) was associated with increased grain plumpness. With the aid of a dense array of single nucleotide polymorphisms (SNPs) and EST-derived SSR markers,a total of nine QTLs were detected across the two populations. Of these, a single major locus on the short arm of barley chromosome 5H was consistently linked with trait variation across the populations and multiple environments. The QTL was independent of flowering time andexplained between 5.4 and 15.4 % of the variation observed in both populations, depending on the environment, and although a QTL 9 E interaction was detected, it was largely due to a change in the magnitude of the effect, rather than a change in direction. The results suggest that loss of green colour during grain maturation may be underthe control of a simple genetic architecture, but a careful study of target populations and environments would be required for breeding purposes.